0,0,0',0'-Tetramethyl 0,0'-thiodi-p-phenylene phosphorothioate is disclosed in U.S. Pat. Nos. 3,317,636 and 3,459,856 issued May 2, 1967 and Aug. 5, 1969 respectively, as an insecticidal agent. This compound has been used by the armed forces in the form of powder and spray formulations for delousing humans and has been added to potable water in the form of discrete granules to control of mosquito larvae. In addition, it has been prepared as rubber pellets and plaster of paris cubes which were floated in water at breeding sites for mosquitoes. However, these latter preparations have not been especially effective for mosquito control.
Among the references which relate to the use of 0,0,0',0'-tetramethyl 0,0'-thiodi-p-phenylene phosphorothioate as an insecticidal agent are: (1) J. T. Whittaw, Jr., E. S. Evans, Jr. U.S. Army Environmental Hygiene Agency, Edgewood Arsenal, Md., J. of Economic Entomology, 61, 889-892 (1968); Entomological Special Study No. 31-006-71, Polymer Formulations of Durshan.RTM. and Abate.RTM. as mosquito larvicides (1970), U.S. Army Environmental Hygiene Agency, Edgewood Arsenal, Md.
2. R. T. Taylor, J. W. Miles, G. O. Guerrant and G. D. Books, controlled release formulations for use against aedes aegypti. Proceedings of the 56th Annual meeting of the N.J. Mosquito Extermination Association, Atlantic City, Mar. 19-21, 1969.
3. J. W. Miles and J. E. Woechst, "Formulations for Controlled Release of Abate in Water", Pesticidal Formulations Research, 1969, Advances in Chemistry No. 86, American Chemical Society, Washington, D.C.
While there have also been previous reports of 0,0,0',0'-tetramethyl 0,0'-thiodi-p-phenylene phosphorothioate incorporated into polyvinyl chloride (PVC), these formulations have differed from those of the subject invention in that such formulations included plasticizers and special plastisol type PVC resin and were used to form plastisols (emulsion resins).
The technique utilized in forming said plastisols requires that the liquid additives disperse the PVC resin at room temperature to form a viscous dispersion which is then fused at an elevated temperature. This plastisol technique requires that a specified plastisol type polyvinyl resin be used, and the fusion occurs at an elevated temperature either after the solution has been poured into a mold or after a hot mold has been dipped into the solution. After fusion the plastisols were evaluated for mosquito control. However, in these tests it is indicated that the plastisols did not release sufficient phosphorothioate compound into the aqueous breeding site of the mosquito larvae to achieve mosquito control.